BToE Skype for Business logon

BToE Skype for Business logon

Hi, do someone know where the BToE (3.7) or the SfB get the Logonname that are autofilled into the Logon PopUp, if the BToE is used? I ask, because the Logonname is filled with DOMAIN\Username but we need now the UPN (Email-Address) because we are using now O365 as Office/Calendar. And now it would be great if you could change it somehow or somewhere! Regards, Oliver